Stereo amp with sub output

The short answer is that you don't need a special sub output. You can use the either the speaker outputs or pre-out outputs.

But if its a stereo amp, then the two speaker outputs are already being used.  As far as using the pre-out, that won't be low-pass filtered right? I assume the sub would apply low-pass filtering but I thought te signal should already be filtered some what.

Thanks 

Some time ago, What Hi-Fi had a group test which was won by a Marantz PM7200, in the "try it with these" feature of that test they ran it with a subwoofer and stero speakers, do you have that magazine? if so it will explain how to wire your sub up.

Hi, No I don't have that article, but I will have a look for it!

Thanks!

You just run a second set of speaker cable to the high level inputs on the sub (assuming it has them) from the same set of speaker bindings on the amp.

Probably you are looking for an amp with built-in bass management and don't want to rely on sub's own low-pass filter? Well, there are plenty. I can't recall from top of my mind, but tell me the budget and may be I can tell you about one or two.

Does the additional load of the sub not cause any problems to the amp?

Only some low-end HTIBs feature an amp with provision for a passive sub. Sub-out in any decent amp would always be pre-out requiring you to add an active sub.

But there is an argument for using active subs fed from the speaker outputs of the stereo amp into the high-level inputs of the subwoofer. It's a phase thing, basically - Richard Lord, founder of REL, once gave me a very detailed explanation why it's best at a Gramophone awards dinner, but as it was an awards dinner I'm afraid I couldn't remember the details the next morning, let alone now...

But no, this kind of connection doesn't put any significant extra load on the stereo amp. 

Andrew, that will be something good to know. I believe in knowing 'all-sides of a story' rather than
believing 'what I know is true'.

Doesn't sound good to me, you using the left or right speaker? not both otherwise you'll bork your amp. In the absence of any pre-outs or dedicated sub output I would split off the sound sources signal and pump that into your sub. You've got that left or right issue again though. I'm pretty anti sub though... unless you have two... integrated into your speakers... making them floorstanders...lol.

Thats what always got me. you are using one speaker to drive two outputs (stereo). Sure, you stereo image is kinda irrelevant at sub frequencies, but the relative phases of the bass between the two channels most certainly is not. Picture this: You have a stereo delay on a bass guitar sound, giving it that sort of 'behind you' sound.. ish. Anyway, the waveforms are 180 degrees out of phase with each other. On a normal 2 speaker setup you get the bass. On a setup where you simply add the two channels together and remove the treble to produce the bass you end up with... nothing.

Of course, this is an extreme example and I'm not 100% sure how 2 channel audio is turned into a single channel for bass... but I don't see how problems with waveform phases can be got around without using multiple bass drivers and two amps inside the subwoofer.

I think I'm lacking some fundamental knowledge about how a sub output is created perhaps...

Most subs take the output from both speakers. It would be easy enough to connect a resistor from both speakers to create a mono bass signal. They also usually have a phase switch or variable control to correct any cancellation due to phasing errors.

Variable phase control would be nice, but it's only gonna be perfect if it dynamically alters the phase switching itself to account for the potentially random phase situations it will suffer when playing music. I don't like em... (subs) and personally, I *can* tell which speaker that loud bass note is coming from, without looking at the cones... so I think the stereo image not being effected argument isn't quite right either.

Most of all though, I hate subs because of the tacky 5.1 systems you see for sale everywhere... the ones that have subwoofers reproducing the audio frequencies right up to like 500 hz, then these tinny little pea sized satellites doing the rest.

A sub is for bass, not for disgrace

Now when you have a 5 or 7.1 system with a dedicated subwoofer channel... well that's a different story entirely. If I wanted to find a cheap way to whack a load more bass into my stereo system, I would opt for the cheaper subwoofer option, but get two, one for each channel;)

Surely the "cheap, tacky" 5.1 systems still have a dedicated sub channel?

Why do you hate these systems so much?? I assume noone has forced you to buy or even listen to one of these systems so live and let live I say. You are lucky enough to have a pretty formidable system but I presume these cheap systems are aimed at those that cannot afford the high end gear you approve of.

I dont like the snobbery that occasionally these forums attract.

Apologies if i've misunderstood your argument.....